The leading cause of lower back pain arises from rupture or degeneration of lumbar intervertebral discs. Pain in the lower extremities is caused by the compression of spinal nerve roots by a bulging disc, while lower back pain is caused by collapse of the disc and by the adverse effects of articulation weight through a damaged, unstable vertebral joint. One proposed method of managing these problems is to remove the problematic disc and replace it with a prosthetic disc that allows for the natural motion between the adjacent vertebrae (“a motion disc”).
Prior to inserting the disc, however, the surgeon typically desires to insure that the properly sized implant has been identified for the particular patient. To this end, trial implants are commonly included within the instrument sets that allow the surgeon to temporarily insert the trial into the intervertebral disc space and assess whether the height and footprint of the trial would be appropriate for the actual implant to be inserted. Typically, a large number of trials are supplied in an instrument set, with each having a distinct height, lordotic angle and footprint.
US Published Patent Application No. 2004/0143332 (“Krueger”). discloses both a trial spacer and trial endplates. However, the trial endplates appear to be designed to engage to an inserter instrument that is then positioned within the disc space. See Krueger at [0154]. Therefore, it appears that Krueger teaches a dynamic trial, wherein the operator can vary the distance between the trial endplates by varying the force on the instrument.
US Published Patent Application No. 2004/0167537 (“Errico”) also discloses a dynamic trial, wherein the operator can vary the distance between the trial endplates by varying the force on the instrument.
US Published Patent Application No. 2004/0236342 (“Ferree”) discloses a modular articulating trial, wherein the articulating nature of the trial allows the relative angles of the trial endplates to vary with the orientation of the opposing natural vertebral endplates. See Ferree at [0097].